-- What can I do for you? I want MP4 for my daughter.A. aB. anC. theD. /

问题补充：

-- What can I do for you?

-- I want MP4 for my daughter.

A. a

B. an

C. the

D. /

答案：

A. a

(答案→)B. an

C. the

D. /

解析：考查冠词的用法。不定冠词有a和an两种：a用于辅音音素开头的词前，an用于元音音素开头的词前，MP4的发音是元音因素开头的，故前用不定冠词an，选B。